Norris RX camshaft update

After last weekends opportunity to open up the throttle in the back country and finding my combat engine would only go to 80 mpg, I did a really good set up with starlett dial indicator directly on the valves and got a very accurate setup with a large degree wheel on the drive side of the crankshaft. Here are the result
Left at .020 tappet clearance per Norris spec sheet
Intake .410 lift
Ex .380 lift

Right
Intake .405 lift
Ex .377 lift

Norris spec sheet states .424 lift intake at .006" tappet clearance and .425 lift at .008" exhaust
With valve clearance at running spec right side is .424 intake/.392 exhaust.

By the way the camshaft is marked "RX".

Cam timing was pretty much right on to Norris spec 82BBDC open, 54 ATDC close exhaust and 54BTDC open, 82ABDC close for intake...within a degree.

I think my previous mistake was setting the tappets at .012". Reset to .006/.008 and will recheck the timing before taking another run. Interesting that for comments that the RX is a full race cam, it has the same exhaust lift and a bit less intake lift compared to the combat cam. Also the duration at 316 is less than the combat 328 duration. Not such a radical cam after all.

illf8ed said:

After last weekends opportunity to open up the throttle in the back country and finding my combat engine would only go to 80 mpg
Also the duration at 316 is less than the combat 328 duration. Not such a radical cam after all.

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That is the best fuel mileage I ever heard of anyone getting with a Commando, and you are going for even more, great.

Lift is not really an indicator of a camshafts personality, but duration is much more so. You can not compare the duration of two different camshafts unless it was measured at the same valve clearance on both cams. If Norris measured the duration of their cams while using more clearance than Norton did for the published Combat specs then comparing them is invalid.

The more I read 2S reports and see the graphs the more I'm impressed by 2S. I suspect to get better performance out other 'hotter' cams requires more CR and other flow helpers and a tendency to rpm addiction.

2S


RX

beng said:

illf8ed said:

After last weekends opportunity to open up the throttle in the back country and finding my combat engine would only go to 80 mpg
Also the duration at 316 is less than the combat 328 duration. Not such a radical cam after all.

Click to expand...

That is the best fuel mileage I ever heard of anyone getting with a Commando, and you are going for even more, great.

Lift is not really an indicator of a camshafts personality, but duration is much more so. You can not compare the duration of two different camshafts unless it was measured at the same valve clearance on both cams. If Norris measured the duration of their cams while using more clearance than Norton did for the published Combat specs then comparing them is invalid.

Click to expand...

Yea I do have an issue with typos....mph not mpg.

illf8ed said:

Interesting that for comments that the RX is a full race cam, it has the same exhaust lift and a bit less intake lift compared to the combat cam. Also the duration at 316 is less than the combat 328 duration. Not such a radical cam after all.

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It probably depends on who is doing the commenting about a 'race' cam.
For someone used to sidevalve timings, the Combat probably is beyond a race motor !??!

I can recall taking a Commando head to a car guy (to get a spark plug thread insert),
and he took one look down the inlet tracts and whistled in admiration.
And asked what it was off...

can recall taking a Commando head to a car guy (to get a spark plug thread insert),
and he took one look down the inlet tracts and whistled in admiration.

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I had the same experience two years ago when I took my head to a top engine shop for a little valve grinding

their head guy wrote on my bill "very nice hemi combustion design, is it a Norton head?"

pretty cool

Some one this forum commented the RX was a full race can as context with Commando engines. Made me wonder if I might have gone too far. When compared to the combat cam seems less radical. My goal is only to get the Norris cam working properly which means the engine should pull well passed 100mph....21T gearbox sprocket.

So far cam timing is right on, timing is set to 30 degrees BTDC and tappet clearances .006 intake/.008 exhaust. RITA ignition is working properly. Using .240 main jets with good tan color on the plugs.

It seems to me that if a Commando won't pull over 80MPH there's something more seriously wrong than a couple of degrees of cam timing or a couple of thou of valve clearance.
You seem to have the other stuff worked out.. plug colour seems good, ignition timing right, but my feeling is that something else is wrong.

I thought the RX cam was just a 15/16 cam.

illf8ed said:

Some one this forum commented the RX was a full race can as context with Commando engines.

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Looking at the pair of graphs for the two cams and saying that they look the same is something that my wife would do, the one that told me she saw a bike "just like yours on Route 20" once. I said stunned "really? you saw a 1961 Norton Manxman?" I was stunned until she said, "well it was a blue motorcycle". She will also ask me things like if that car is a Cadillac while looking at a Ford Escort.

If you look at all the graphs for all Norton cams they do not look much different when you get into the later ones or the high performance jobs, so it is the subtle differences that do make a difference.

The RX graph might have little lines that stop and start roughly where the Combat lines do, but it looks to have more effective duration and overlap, it gets the valves to various points more quickly. I would definitely think that it would be more of a race cam than the Combat. Again, lift has nothing to do with the rpm range of a cam as long as it is all stuffed inside a certain duration. The real trick to designing a flat tappet cam is to fit a lot of lift into a short duration without creating a geometry and acceleration that makes the tappet leave the lobe at useable rpms. The higher the lift for a certain duration and overlap the more power you might make at lower and reliable rpms.

Did you ever actually check the static compression ratio of this Combat engine? The volume at BDC vs. TDC.? It is important as with a big cam you need the compression to keep your mid-range power. The static preserves the power low and in the middle when the overlap and duration is trying to leak it out the ports and the dynamic gets it back at high rpm by working with a tuned exhaust and intake tract, which by the way you don't have....

The stock 32mm Norton heads are probably the worst ports Norton put out, not as friendly to mid range as the standard Commando heads and not worth pursuing, I would never go out of my way to own a Combat or RH4 850 head.

So throwing a hotter cam into a street engine with stock exhaust and intake tract and whatever compression sounds like it would run like shit and lo and behold it does.

If you do have close to the stock static compression, my guess is that if you added an inch or two to the intake manifold and put some long carb intake bells on along with long open reverse-cone meggas it would transform the power of the engine.

You have created larger compression leaks for your engine at low and middle rpm ranges, and do not have the tuned intake and exhaust tracts to work with the cam to get anything at high rpms, so I am not surprised your engine runs like shit.

T.C. Christenson should know a think or two about Norton tuning. He talked to me 20 years ago about the Norris grinds. He said "R" for hot street with mufflers, RX for track with meggas, D for crazy Drag bikes. He specifically said that the RX would not run good with mufflers and I would take his and other real racers and tuners word for it over my wife or some other layman looking at a couple of graphs someone showed them.

I agree. I put a Norris "R" cam in a otherwise stock 1969 Commando and it ran like a thief in the night. I have a 1972 Combat with a Web 12a cam that is not nearly as fast as my 1969 was.

Yep sirs, even half a Commando standard engine will push one over 80 mph though not hard to hang on to getting there, so something like 50%+ off wrong. Over cammed, lowish CR will be doogie doo at low speeds/rpm but should wake up enough at hi rpm speed to pull over the ton. Likely only takes 25-ish hp to reach the ton on our size cycle. Interesting mystery that could happen to any of us, so certainly one day will figure why.

The combat graph in this thread has 3" radius on the lifters, as indicated at the top of the graph. That should calm it down a bit compared to flat lifters.
Bill G

" Yep sirs, even half a Commando standard engine will push one over 80 mph "

Id considered the 750 pretty much two 350 Manxes , in one chassis .
Comparable bore & stroke & R.P.M.s , so cant be to useless for something .

More to the point , getting each cylinder breathing as per 40M needed for a fair crack of the whip .

Still working on it. Will post if and when I get a solution. Desired result is comat performance with no engine knock.

A lot of stuff thrown out, but if I can take you comment you say was made by TC regarding the RX as fact, then my take away is replace the RX with a combat cam. I'm going to continue playing with it a bit more before giving up.

Thanks

T.C. Christenson should know a think or two about Norton tuning. He talked to me 20 years ago about the Norris grinds. He said "R" for hot street with mufflers, RX for track with meggas, D for crazy Drag bikes. He specifically said that the RX would not run good with mufflers and I would take his and other real racers and tuners word for it over my wife or some other layman looking at a couple of graphs someone showed them.[/quote]

To offer up some encouragement before starting from scratch is that The best final engines in my boats, van's and Nortons were very disappointing frustrating in the beginning and through many tweakings that didn't make much difference till one more thing diddled >> Oh My YES. I've had outboards 2tokes and my P!! and pre-Peel and Ms Peel all wake up dramatically when exhaust opened up engough so make some neighbors and their pets start barking and get back to us.

hobot said:

To offer up some encouragement before starting from scratch is that The best final engines in my boats, van's and Nortons were very disappointing frustrating in the beginning and through many tweakings that didn't make much difference till one more thing diddled >> Oh My YES. I've had outboards 2tokes and my P!! and pre-Peel and Ms Peel all wake up dramatically when exhaust opened up engough so make some neighbors and their pets start barking and get back to us.

Click to expand...

Thanks...that's what I'm hoping for.

'You have created larger compression leaks for your engine at low and middle rpm ranges, and do not have the tuned intake and exhaust tracts to work with the cam to get anything at high rpms, so I am not surprised your engine runs like shit.'

What he said. However it is not 'compression leaks' it is lack of harmonic.
The timings affect the standing waves in the inlet and exhaust tracts, the lift affects the power output at all revs, as does the compression ratio. If you are running with exhaust back pressure due to the muffler or the wrong pipe length the system may not work well, over the whole rev range the cam is intended to cover.
I always use Triumph E3134 race cams as a benchmark. From memory the prescribed timings are:
IO BTDC 52
IC ABDC 72
EO BBDC 72
AC ATDC 52
The recommended straight open pipe length used is 38 inches. The inlet length is 8 inches.
In a 650 Triumph that gives a power band which comes on strong at 4,000 RPM and ends at 8,000 RPM, regardless of compression ratio. If you use those cams in a standard 650 Triumph motorcycle, it will still work and give the same power band, it just won't be as good. I suggest it is all about harmonics and back pressure. You have a standing wave in the inlet tract, and another in the exhaust. If the exhaust is restrictive, the gas flow is inhibited, so the system fails to establish the harmonics. The lift rate (profile) of the cam can affect whether the valve train can follow it at high revs. If the opening rate is too high, the valves might tangle with the pistons if the springs cannot maintain control. If the closing rate is too high, the head might be popped off a valve. As far as porting is concerned, it is important to recognize the torque characteristics you need, and your gearbox and the roads you ride on affect that. You can enlarge the inlet ports to get more top end, and with a race cam, the top speed of the bike will be greater. However if you lose the midrange, you will find it much more difficult to outride other riders when you are on tight twisty roads or many race circuits. Also the bike might not accelerate as fast as it could due t o lack of mid-range pulling power. I tapered the inlet ports on my 850 motor from 34mm down to standard over the first 25mm of the port. The amount of gearing it pulls is absurd, and it accelerates up through the rev range very quickly even pulling that gearing. If you keep the gas speed in the inlet port high at the valve, that can be a good thing.

A lot of the old sows used telescopeing tailpipes to vary ( for conditions ) & ascertain powerband layout .
you have to fix a few variables as a matter of course , or it gets too like infinately . Which might take a while to sort .

The Great Horay service notes mega , on a 2-1 , isnt to loud ( unbaffled ) . Unless youre at High Throttle or RPMs .
Actually , high revs it can get more a contiuous note rather than sepearte peaks . Which rattle windows .

Made from 14 Guage , to reduce resonance , and that header wrap wrapped , tightly , with adheshive .
The ides to get the sound waves multiply overlapped . So the beats not offensive . This way the Exhausts ' Un Baffled ',
as good as unmuffled , if done something like right .

The old Wassel Megas , that look like the Lafrancontis or whatever , with their perforated baffles , if youre prepared to not
give it the grief in suberbia , are most melodious & efficent . And made of STEEL , not TIN .
However , if you F it up , warm , and it Catches starting as youve pushed youreself up & the throttles gone way up ,
as the combustion catches at the third ' FIRE ' : while a old Ladys walking directly behind in the middle of the Plate Glass
shop Front , shell need a good grib to hang onto her shopping bags .

So wait till alls clear aft before lighting , and all clear forward before engaugeing drive . Or things may get a bit ahead of you

Think you need to bludge a set of mangey looking old header pipes to cut & play around with .

There were some marevellous Dirt Track trumpy rev. cone megas , around 15 in. long .
After Market U.S. things . That give wonderfull Acoustic Propeties .
You can really HEAR whats going on and how its working , for twin pipes .
You should look there ? T.T. stuffd .
The reason people fitted slash cuts , lttle megas & those horrible tulip things , is it let out more than just the BARK .